Relationship between structure and retention index for N-substituted amides of aliphatic acids on a non-polar column

Abstract

The retention indices of 100 amides of aliphatic acids (R 1-CO-NHR 2) divided into ten series depending on the substituent R 1 at the carboxylic carbon atom or the substituent R 2 at the nitrogen atom, each containing the same set of ten substituents at the second site, have been measured on a non-polar GE SE-30 column. A relationship between the retention index of the amide and the number of primary, secondary, tertiary and quaternary carbon atoms in the molecule has been found. The retetion indices obtained were correlated with those of corresponding simple model compounds, such as substituted hydrocarbons (R 1H and R 2H) and amines (R 2NH 2). The good linear correlations obtained indicate that, for prediction of retention indices of amides the correlation method should be used instead of the additivity rule. Retention indices of amides were found to obey a two-parameter linear equation with the retention indices of corresponding model compounds as independent variables.